The invention relates to improvements in power trains for motor vehicles, and more particularly to improvements in power trains with overspeed protection wherein the clutch is operated in dependency upon the rotational speed of the prime mover and is automatically disengaged or operates with slip when the RPM of the prime mover (such as an internal combustion engine) exceeds a preselectable threshold value during engagement of the clutch.
German patent No. 197 45 677 C2 discloses a motor vehicle wherein the prime mover is operatively connected with an automatically actuatable clutch in such a way that the engagement of the clutch is regulated in dependency upon the rotational speed of the prime mover and of the clutch plate or clutch disc. The rotational speed of the prime mover is monitored in order to ascertain whether or not it exceeds or drops below predetermined upper and lower limits The clutch is disengaged automatically, or is operated with slip, when the rotational speed of the prime mover exceeds the upper limit or drops below the lower limit.
The just described prior proposal exhibits several drawbacks. Thus, if the power train of the motor vehicle employs an automated transmission, a malfunctioning of the actuator for the transmission and/or improper operation of the clutch regulating or actuating means and/or a defectiveness of the system which monitors the selected gear of the transmission causes the transmission to automatically shift into a lower gear in lieu of shifting into a higher gear, and such undesirable shifting is not signaled to the operator of the motor vehicle. If the undesirable shifting of the transmission into a lower gear remains unnoticed, the clutch remains engaged until the indicator of the speed of the prime mover detects the resultant overspeeding of the prime mover. The next step involves a disengagement of the clutch. However, and depending upon the dynamics of the clutch engaging system, even a short-lasting temporary overrevving of the prime mover can entail extensive damage thereto. Furthermore, an overspeeding of the prime mover can result (at least under certain circumstances) in the application of excessive braking torque to the wheels of the motor vehicle.